The present invention relates to a matte ink composition for use in lithography printing. More particularly, the present invention relates to a matte ink composition having superior adherence properties for printing directly onto a gloss surface. Further, the present invention relates to a method of forming a superior matte-gloss contrast finish without the need for specialized UV equipment and procedures.
In a lithography printing process, one or more printing plates are used to transfer ink to a printing substrate, with one plate for every ink composition used. A lithography plate has two regions: an oleophilic image area for receiving an oil-based ink and an oleophobic non-image area for receiving a water-based, non-imaging solution, known in the art as a xe2x80x9cfountainxe2x80x9d solution. During the printing process, the ink and fountain solution are applied to a printing plate and allowed to gravitate to their respective areas. The ink can be transferred directly to the substrate or it can be transferred to an intermediate xe2x80x9cblanketxe2x80x9d cylinder and subsequently transferred to the substrate, the latter being known in the art as offset lithography printing.
As with other printing inks, lithography printing inks are designed according to several criteria, including the desired visual characteristics of the printed material, the printing process which will be used, the drying conditions of the ink, the substrate to which the ink must adhere, and the wear resistance of the ink. While an ink may include various pigments to achieve a desired visual effect, an ink may also be designed to achieve other visual effects, such as a gloss or matte (dull) effect. A gloss effect occurs when incident light is reflected and a matte effect occurs when incident light is scattered. A popular visual effect is a combination matte-gloss contrast finish, which is particularly popular for magazine, book, and periodical covers. In this case, the matte and gloss coatings, both of which are preferably transparent, are printed over the pigmented ink coatings, if present.
To achieve a combination matte-gloss contrast finish according to present lithography printing methods, a substrate is first printed with a matte ink composition in selective areas where a matte effect is desired, after which, a gloss ink composition is printed onto the substrate in selective areas where a gloss effect is desired. The matte and gloss coatings normally do not overlap. While the matte and gloss coatings can be applied immediately following application of any pigmented ink(s), it is preferable to apply the matte and gloss coatings after the underlying coatings have dried. Nonetheless, in either case this process produces only a moderate contrast between the matte and gloss surfaces.
To achieve a superior matte-gloss contrast finish, another process has developed in which the substrate is first coated with a plastic matte film lamination. Because inks do not readily adhere to plastic films, a specialized gloss ink is used wherein the ink is selectively xe2x80x9cspotxe2x80x9d coated thereon and cured to the matte surface via ultra-violet (UV) radiation. Although this UV process produces a greater matte-gloss contrast than that seen from the offset lithography process, the gloss coating is not very durable and has a tendency to detach from the matte surface if the coated substrate is stressed, for example, by folding or creasing. Moreover, UV curing processes require specialized equipment (e.g. photopolymer plates or silk screens) and procedures that are both time consuming and expensive. Consequently, most lithography printing companies cannot afford the specialized UV equipment and must send their products to a printing company having the specialized UV equipment for application of the gloss coating, a detour which substantially increases production time and costs.
Other problems with the UV process includes that the photopolymer plates and silk screens are very coarse and it is extremely difficult to print fine detail. Accordingly, the detail available with the UV process is substantially inferior than that available with lithography printing. Also, with silk screens, it is difficult to regulate the amount of UV coating that is being applied to the sheet. Finally, since the UV process is somewhat different than the lithographic process, it is difficult to achieve proper registration between the gloss coating and the graphics that have been lithography printed on the substrate.
Accordingly, what is needed is a novel ink composition and method of use which overcome the problems in the prior art and which provide a superior matte-gloss contrast finish without the need for specialized UV equipment and procedures, wherein the overlay finish coat will not detach from the base finish coat when stressed.
It is an object of the present invention to provide a matte ink composition for use in lithography printing.
It is another object of the present invention to provide a matte ink composition which has superior adherence properties for printing directly onto a gloss surface.
It is another object of the present invention to provide a matte ink composition which will not detach from a gloss surface when stressed, for example, by folding or creasing.
It is another object of the present invention to provide a method for producing a superior matte-gloss contrast finish without specialized UV equipment and procedures.
It is another object of the present invention to provide an ink composition and method for producing a superior matte-gloss contrast finish having substantially finer detail than matte-gloss finishes available by prior art methods.
These and other objects of the present invention are accomplished with a novel matte ink composition and method for using the composition to produce a superior combination matte-gloss finish. The matte ink composition comprises (1) an oleoresinous component, acting as both a vehicle for the other ink components and a quickset agent to promote a durable, wear resistant coating when dried, (2) a matte agent to impart a matte finish, (3) a cobalt catalyst to accelerate drying of the composition, and (4) an etching agent to condition the gloss surface to promote adherence of the ink composition to the gloss surface. Optional ingredients include (5) a plasticizer to promote flexibility of the dried ink composition without cracking or blistering, (6) a manganese drying agent to aid in drying of the composition, and (7) a wax compound to increase rub resistance and to impart slip.
To prepare a matte-gloss finish according to the present invention, a printing substrate is first coated with a gloss film lamination and, after the gloss coating has adequately dried, the matte ink composition of the present invention is lithography printed onto the gloss surface. It is important to note that the matte ink is printed over the gloss film lamination, which is opposite the UV method in which the gloss ink is printed over the matte film lamination. This novel matte ink composition provides a superior combination matte-gloss contrast finish without the need for specialized UV equipment and procedures. Thus, a superior matte-gloss contrast finish can be produced with offset lithography equipment and film lamination equipment, thus greatly decreasing the cost and time associated with presently used ink compositions and methods for producing a quality matte-gloss finish. Finally, the matte ink composition of the present invention and its method of use allow substantially finer matte-gloss contrast detailing than attainable by the presently used UV ink compositions and methods for forming a matte-gloss finish.
These and other objects and advantages of the invention will become apparent from the following detailed description of the preferred embodiment of the invention.
The ink composition of the present invention finds primary use in offset lithography printing, however, the composition and method may be used or modified for application in other related printing methods, such as direct plate to substrate lithography printing or letterpress printing, and, therefore, the present invention includes any foreseeable modifications for use in related printing methods. A detailed description of offset lithography printing and the ink compositions used therein will not be set forth herein, however, numerous publications are available that teach in detail the equipment, procedures, and materials used in an offset lithography printing operation. Two such publications are The Printing Ink Manual, 4th Edition (1988), published by Van Nostrand Reinhold (International) Co. Ltd., and The Lithographers Manual, 7th Edition (1983), published by The Graphics Arts Technical Foundation, Inc., both of which are incorporated herein by reference.
The major component of a lithographic ink composition is known as a lithographic ink varnish or vehicle, which comprises a resin and an oil component. The oil component primarily acts as a carrier for the resin component, although it has other actions as well, such as an effect on the drying time of the ink composition. The resin component binds the various ink components together and to the substrate once the ink is dried. The resin also imparts other properties, such as hardness, wear resistance, and drying time. Lithographic ink varnishes are comprised of two main classes of inks based on the method used for drying the ink: (1) an oleoresinous ink composition, which is dried by oxidation, absorption, or solvent evaporation, and (2) an acrylic ink composition, which is dried by radiation curing, such as UV or electron beam. The present invention is directed to oleoresinous ink compositions.
The resins and oils in the oleoresinous varnish component of the present invention may include any natural and/or synthetic resins (e.g. phenolic, alkyd) and oils (e.g. linseed, tung) appropriate for use in lithographic inks. The matte ink composition of the present invention comprises at least 4 ingredients: (1) between 75-90%, preferably 80-85%, of an oleoresinous component, which acts as both a vehicle for the other components and a quickset agent to promote a durable, wear resistant coating when dried, (2) between 10-25%, preferably 15-20%, of a matte agent, preferably fumed silica, to impart a matte finish, (3),between 0.1-10%, preferably 1-2%, of a cobalt catalyst to accelerate drying of the composition, and (4) between 0.1-10%, preferably 1-3%, of an etching agent, preferably isophorone, to condition the gloss surface to promote adherence of the ink composition. An excessive amount of the oleoresinous component prevents adequate inclusion of other ingredients, thereby reducing adhesion, matte effect and drying time, and an insufficient amount results in poor wear resistance. An excessive amount of the matte agent interferes with adhesion, wear resistance, and drying time, and an insufficient amount results in inadequate dullness. An excessive amount of the cobalt catalyst results in unreacted catalyst, thereby interfering with drying, and an insufficient amount slows drying time considerably. An excessive amount of the etching agent interferes with drying and an insufficient amount results in poor adherence to the gloss surface. The etching agent in the preferred embodiment is isophorone, although other etching agents may be used with the present invention, including acetone, cyclohexanone, diacetone alcohol, ethyl acetate, isopropyl acetate, methyl ethyl ketone, methyl iso-butyl ketone, n-butyl acetate, toluene, and xylene. Optional ingredients include (5) a plasticizer to promote flexibility of the dried ink composition without cracking or blistering, (6) a manganese drying agent to aid in drying of the composition, and (7) a wax compound to increase rub resistance and to impart slip.